The present invention is related to microprocessor based electro-pneumatic brake systems for railroad freight cars having a pneumatic emergency backup brake with a load control function provided by the microprocessor.
In electro-pneumatic brake systems, a pneumatic emergency backup brake is desirable from the standpoint of bringing the train to a safe stop in the event of a power failure. A double check valve device may be employed to separate the two brake control systems such that the system producing the higher pressure prevails in controlling the car brakes. In such an arrangement, the pneumatic emergency brake becomes effective in response to a reduction of brake pipe pressure, such as in the case of a train break-in-two, for example. This is typically accomplished by having the solenoid valves in the electro-pneumatic brake system configured to release the electro-pneumatically controlled brake cylinder pressure in a deenergized condition.
It is desirable in a microprocessor based electro-pneumatic brake system to utilize the microprocessor to monitor the car load condition and regulate the brakes accordingly. It is also desirable to regulate the pneumatic emergency backup brake according to the load condition of the car. Such load control of the railroad freight car brakes protects the car wheels from damage due to wheel slide.
It will be appreciated that where the pneumatic emergency backup brake employs a load control function under control of the microprocessor, such a power failure, as would occur in the case of a train break-in-two or such as would be caused by a microprocessor malfunction, renders the car load control ineffective to properly regulate the emergency backup brake. Consequently, light or empty cars in a train could be overbraked during emergency backup brake operation, causing wheel slide and the aforementioned wheel damage that results from such condition.